Catheter ablation has become the treatment of choice for many types of arrhythmias largely because it is curative, safe, and relatively inexpensive. However, due to limited tools for mapping complex arrhythmias, catheter ablation is much less effective when used to treat arrhythmias that are not constrained by known anatomic barries. The goal of this research is development of a novel system for endocardial mapping, one that combines anatomical information provided by fluoroscopic images with functional information provided by intracardiac electrograms. This system will provide clinicians with a powerful tool that will assist them in accurately mapping complex arrhythmias. During Phase I, a prototype version of the system was developed and installed in a clinical setting. The prototype system demonstrated the feasibility of the concept and the primary data processing algorithms. During Phase II, a full-featured, real-time version of the system will be developed and installed in the cardiac electrophysiology laboratory. The clinical utility of the system will be evaluated during a number of arrhythmia mapping procedures and used as a basis for developing a new mapping methodology. PROPOSED COMMERCIAL APPLICATION: The primary commercial application for this work is in cardiac electrophysiology workstations. The technology developed under this program caould be incorporated in existing workstations or marketed as a stand-alone system.